Specific solvatochromism of the prototypical olefin complexes (.eta.2-TCNE)M(CO)5 (M = chromium, tungsten) resulting from n and .pi. donation of aprotic solvents toward the .pi.-acceptor ligand

The solvatochromism of the well-separated long-wavelength charge-transfer bands of the title complexes was studied in 36 aprotic solvents and in dichloromethane solutions durene and hexamethylbenzene. The observed effects may be interpreted consistently in terms of strong n- and π-donor contributions from the solvents